If a woman has a medical condition that will make pregnancy dangerous for her, an abortion may be beneficial. This is especially true of an ectopic pregnancy (in the fallopian tubes) - you must have an abortion to end this type of dangerous pregnancy.
If the fetus is diagnosed with severe birth defects or with a condition that will most likely result in death shortly after birth, an abortion can prevent suffering.
In a multiple pregnancy (twins or more) an abortion of one of more fetuses (called "selective reduction") can prevent complications and result in the healthier birth of the remaining fetuses. This is usually only offered in triplets or more.
If the pregnancy is unwanted and the mother feels she will be unable to adequately care for her child or that she may harm her child, an abortion can prevent the child from suffering.
If the pregnancy is unintended, an abortion can help a woman continue with her education, career, or other goals without the interruption of a pregnancy and/or caring for a child. If a woman already has other children, she may not feel she has the resources to care for another child.
If the pregnancy was a result of a raping, it might be uncomfortable and painful for the woman to bear that child. That child would always carry the hurt of that memory for the mother.
Cons
All abortions carry some risk. Most early abortions can be performed with medication only; later abortions must be done surgically and all surgery carries some risk.
Some studies have found that women who undergo an abortion have higher rates of depression and higher rates of miscarriage in later pregnancies.
Many people feel that an abortion ends a life or potential life. A woman may have feelings of guilt after an abortion or wish she had continued her pregnancy.
There are many people trying to adopt a baby. Your baby may be able to live a happy, full life if you are willing to continue your pregnancy and allow the baby to be adopted. In most adoptions you are able to choose the future parents and have contact with your child if you wish. The future parents may even pay your expenses and medical bills.